This invention relates to apparatus and method for spraying water-borne emulsion topcoats which are particularly useful in the furniture finishing art but also have application in other arts where water-borne emulsion topcoats are sprayed on to provide high quality surface finishes.
Currently it is common in the furniture industry to use solvent-based materials for topcoat finishes, one or more topcoats being sprayed on by skilled personnel to achieve the desired finish appearance. The topcoats are normally applied after one or more undercoat treatments have been applied in well known manner, such as stain, washcoat and sealer applications. It is important, especially in high quality furniture, that the topcoat provide a smooth, high gloss surface with excellent clarity. Solvent-based topcoat materials have been preferred for this purpose due to their consistency in imparting these and other desired characteristics to the finish surface.
One problem with using solvent-based materials is that, on drying, the solvent is released into the atmosphere as an undesired vapor causing resultant air pollution. Government regulations are being proposed that would severely limit the level of permissible solvent vapors released into the environment. In order to comply with these regulations, it would be necessary to install complex and expensive equipment to trap and remove the solvent vapors from the air. Consequently, efforts are being made to develop water-borne emulsions to be used as topcoat finishing materials in order to reduce the presence of the solvents to such an extent that the air quality regulations can be met without the need for expensive air pollution control equipment in the plant.
Although water-borne emulsions have been developed for spray-applied furniture topcoats that impart desired characteristics to the finish surface such as hardness, elasticity, resistance to water or alcohol staining and the like, one persistent problem that heretofore has not been satisfactorily resolved is the inability to consistently realize the high gloss and good clarity required for high quality finishes. In general, the water-borne emulsion topcoat has been found to impart a surface appearance that is duller and less clear than is preferred and the degree of unsatisfactory result tends to be susceptible to variations in the environmental conditions under which the spray coating is applied.
Comparative analysis of conventional solvent-based lacquers and water-borne emulsion coatings has shown that the water-borne emulsion contains a myriad of air bubbles entrained in the dried film while the lacquer is generally free of bubbles. The presence of these bubbles causes light scattering in the film which imparts a hazy and sometimes milky appearance to finish. Additionally, small pin holes resulting from air bubbles that have not completely escaped the film along with a micro-wrinkling effect result in a reduced gloss. Varying the formulation of the emulsion has not provided a satisfactory solution to eliminating these bubbles which occur as a result of entrained air caused by the spraying process.
It is, therefore, an object of the present invention to provide apparatus and method for spraying water-borne emulsion topcoats that substantially improves the clarity and gloss appearance of the resulting finish coating.
It is a further object of the invention to provide apparatus and method of spraying water-borne emulsion topcoats which is readily adaptable to existing furniture finishing processes without the need for special controlled environment conditions in the finishing area of the plant.